Tow target



M. BACHNER Jan. 17, 1956 TOW TARGET Filed Oct. l, 1951 United States Patent() Tow TARGET -Martin-.Bachner lottstvwn, ,Pas ,assignor 4to The Firestone Tire'tSa Rubber Company,` AkronxQhio, acorporation of Ollio This invention relates to banner tow targets for towing throughthe airby an airplane or other suitable means, for target practice -`by `gnnnersv in other aircraft or on the ground. :Targets ofthis typepresent several problems. .`hey must be of a material whichr has minimum drag and ris strong enough to resist tearing orfraying by being towed at high rates of speed, often 300 miles per Vhour or more. Suclitargets arer usually made of a rectangular piece of fabric attached to a suitable tow line for fastening to the towingmeans. -The fabric is preferably Woven from monolilament material in order to avoidV unraveling and twisting characteristic of multilament yarns.

One of the problems encountered in developing tow targets `from monofilamentyarns resides in the'faet that most synthetic monolarnents tendto become brittle at .-the-.low temperatures encountered at high altitudes. Many ,synthetic monofilaments which -have excellent lstrength .and flexibility .at Aordinary air temperatures, 40 4to l,00-.'F.,;.beeome quite brittle, and are `easily broken, at temperatures about 40 F., which is typical at high altitudes. Previously. tried synthetic materials which have been ,especially .plasticized `.to make them flexible at low .temperatures do not have satisfactorystrength at `the .higher temperatures mentioned, and are often quiteflabby at these higher temperatures.

Another problem encountered in the development of the tow targets-has been to produce a fabric having high trapezoidal tear resistance. This characteristic is considered necessary for a successful tow target fabric, in ,order to minimize tears which might result from. air-drag andlalsoprojeetile holes. Many nfatn'i'cswof highstrength rfilaments''have fallen down in this respect, forV reasons knot j clearly`understood. Still another problem encountered in attempts `to use ,Synthetic fabrics in tow targets is to prevent deterioration of the vtargets by action of sunlight and other atmospheric factors. Many synthetic materials exhibit very desirable physical properties when maintained out of sunlight and away Vfromoxidizing conditions, but undergo rapid deterioration whenexposed to the sun and air.

jIt isthereforean object `of 4this invention lto provide van improved tow target -for use yin the air, Ywhich successfully' solves the problems enumerated above. Specifically, it is an object to produce a banner tow target made of fabric woven from synthetic monolament material, the fabric possessing satisfaet'ory strength at all temperatures encountered in actual use, having high trapezoidal tear characteristics, remaining flexible at low temperatures as well as at high temperatures, being substantially unaffected by sunlight and air, and resisting tearing when towed through the air at high rates of speed and when perforated by projectiles. It is also a specific object to provide an economical tow target which may be readily manufactured at low cost. An additional object is to produce tow targets capable of detection by radarscope.

The above and further objects will be apparent in the description of the invention which follows, and in the single sheet of drawing, in which:

firice Fig.- 1 is a schematic side*elevation ,of `a tow target of `the invention ,attached to .a towingy airplane; v

Fig. 2 'is a fragmentary view of lan open weave `square woven fabric for use in the tow target of the invention;

Fig. 3 is a fragmentary view of an open weave lleno fabricfor use in the tow targetuof the invention;

Fig. 4 is a perspective view, partly inseetion, of a foil-coated monolament of a modified embodiment of the inventionrand Y Y i y Fig. 5 is a perspective view, partly in section, Iofka metal-coated monofilament of another modied'embodiment of the invention.

The objects ofthe invention are aeeomplishedby fabri- .eating the tow target fromasuitable Afabric v Woven of polyethylene monoiilament yarn. The polyethylene ,is suitably u nplasticized ,and nmay contain Yno pigments or other compounding ingredients, Valthough suitable pigments may be incorporated if desired.

Although polyethylenehas lpmi/Sid t0 rbe ,quite Vsuccessful inlilm for food vi/rapping, vand other vuses which are satisfied by a relatively vlow strength, somewhat ilabby material, polyethylene `fabric has not heretofore been found acceptable in the textile trade. y.li'elyethylene `fabric generally possesses a softV and somewhat vilabby. feel, when compared with such successful textile'fabrics `asrthose made of monofilament nylon and saran. Also, polyethylene fabric is somewhat sensitive to the high temperatures regularly `encountered, in laundering and. pressing operations, sincepolyethyleneis thermoplastic, even though it is crystalline and orientable.

Inspiteofthese. apparent Vdrawbacks .it ,has been found in accordance .withthe present invention that open weave fabrics, such as those shown in Figs. -2 `and 3, of po1yethylene monolaments -exhibit: ,high trapezoidal tear characteristics, even. though vthe tensile -strength of the mQnQfilament yarnis onlya fraction ofthe tensile strength of nylon or saran yarns. it has also been discovered y,that such polyethylene Vvfabric retains .these desirable tear- `resistant .characteristics over anextremely wide range of temperatures, frombelow -l0,0" F. to more than l10.0 F., even though the `polyethylene filament `contains no added ,plastieizen '.Additionally, it hasbeen proven by actual tests that suchpolyethylene fabric is quite stable in the preseneeof sunlight, and air, Vand does not deuteriorate rapidly as d o similarkfabries of other synthetic monoiilaments.

Polyethylene may 2be,ex'tri-1de'd in known manner to produce a finished ilarnent`l0 having a ,diameterofk approximately 0.0'10 to 0.050 inch, preferably in the range of ,0.019 to0.02'3 inch. The filament may "be oriented,

vand may also be given a supplernfental heat treatment while under Vsome tension in order toireduce shrinkage, if

, ,desired- The fabric may be manufactured in a variety of open weaves, the two weaves yshown in Figs. 2 and 3 being merely illustrative. The locked 4leno weave shown inlFig. 3 .possesses some mechanical advantages over the simple cross woven fabric of Fig. 2, and is a preferred weave. The tow target fabric should be produced with an open weave in order to keep down the weight of the target. The fabric is woven to weigh less than 10 ounces per square yard and preferably in the range of 5 to 7.5 ounces per square yard. The preferred weave is identified as a three-end leno repeating on six picks, which is illustrated in Fig. 3, the warp filaments being identified as lila, 10a and the till or weft filaments as 10b, 10b. A suitable fabric produced from lament of 0.020 inch diameter has not less than l2 warp ends per inch and not less than 11 picks per inch in the filling direction. The fabric is preferably selvaged, a selvage of 1/2 to 1 inch being satisfactory. Such fabric has been found to possess warp and filling breaking strengths of more than 35 pounds 3 per inch, and elongation of over 30% in the warp and over 25% in the filling.

A target is constructed of polyethylene fabric as described, suitably in the form of a banner approximately 6 feet wide and 30 feet long, designated 11 in Fig. l. The banner is attached at one end to a harness i2 connect'ed to a tow line 13v for attaching to an airplane 14 or other suitable towing means.

One example of polyethylene monofilament fabric suitable for manufacture of the tow target was an off balance square woven fabric possessing a fabric thickness of approximately 0.020 inch. The fabric possessed the following physical properties:

Tensile strength (1 inch grab method):

Warp lbs 118 Filler lbs 74 Elongation:

Warp percent 39 Filler do 65 Tear (trapezoid method):

Warp lbs 86 Filler lbs 48 Cold temperature test at 123 F No cracking The fabric of the leno weave shown in Fig. 3 was prepared from monofilament polyethylene yarn of approximately 0.020" diameter. This fabric had the following A banner target was prepared from this leno fabric and was fiown 30 minutes at 25,000 feet and 20 C., and then an additional 30 minutes at 10 C., without showing any appreciable wear.

A similar target in accordance with the invention was flown a total of 17 missions, total fiight time 15 hours, 190 miles per hour average speed, at altitudes of 7,000 to 20,000 feet. At the end of this time the tow target had 640 projectile holes but was still considered satisfactory for further use. Y

Although unpigmented polyethylene filament has been proved to be quite satisfactory in tow targets, it is contemplated that other polyethylene compositions may be used in the invention. For example, carbon black may be incorporated in polyethylene to produce a black filament possessing greater resistance to sunlight aging. Also, conventional organic chemical light and heat stabilizers may be incorporated in polyethylene prior to extruding in filament form. Other colors than black may be incorporated in the polyethylene prior to extrusion, in order to mark the tow target with a distinctive color, or to provide colored filament for weaving a desired design into the fabric to be used in manufacturing tow targets. Fluorescent pigments may be incorporated into or onto the filaments or a portion of the laments of the target to increase its visibility.

By providing polyethylene monofilament with a covering or coating of metal a tow target is produced therefrom which reflects radar waves. This type of target may be used at night or through clouds to provide gunnery practice for an aircraft or ground gunner equipped with a suitable radarscope or similar device. As is shown in Fig. 4, a polyethylene monofilament 15 is covered (or partially covered, if desired) with a spiral wrapping of metal foil 16, aluminum foil being found satisfactory. A tow target produced from fabric woven partially or completely of such foil-wrapped filament is readily visible in a radarscope.

Another modified filament for use in the fabrication of a tow target for radar gunnery practice is shown in Fig. 5. A polyethylene filament 17 is partially or completely covered with a thin layer 18 of metal, as by the vacuum vapor deposit technique. Thus, filament is placed in a high vacuum in which a metal (such as aluminum) is vaporized by means of a high frequency electric discharge, and the vaporized metal is allowed to deposit on and adhere to the surface of the filament.

What is claimed is:

1. An aircraft tow target comprising essentially a sheet of an open weave fabric woven of monofilament polyethylene yarn, the diameter of filament being in the range of 0.010 to 0.050 inch, the weight of the fabric being less than 10 ounces per square yard, the breaking strength of the fabric being greater than 35 pounds per inch in both warp'and filling, a substantial portion of the yarn carrying a thin coating of metal on the surface thereof.

2. A tow Vtarget as in claim 1, in which a substantial portion of the yarn is wrapped in thin aluminum foil.

3. A tow target as in claim 1, in which a substantial portion of the yarn surface comprises a thin adhered layer of metal.

References Cited in the file of this patent UNITED STATES PATENTS 1,730,263 Brooks Oct. 1, 1929 2,210,774 Perrin et al. Aug. 6, 1940 2,238,875 Manson Apr. 15, 1941 2,357.851 Scheyer Sept. 12, 1944 2,458,243 Biddle Jan. 4, 1949 2,511,644 Liss .Tune 13, 1950 2,523,738 Trimbach Sept. 26, 1950 FOREIGN PATENTS 4,389 Great Britain of 1888 OTHER REFERENCES The New Fibers, Sherman and Sherman', D. Van Nostrand Co., Inc., N. Y. C. Copyright 1946, pp. 131-141. 

1. AN AIRCRAFT TOW TARGET COMPRISING ESSENTIALLY A SHEET OF AN OPEN WEAVE FABRIC WOVEN OF MONOFILAMENT POLYETHYLENE YARN, DIAMETER OF FILAMENT BEING IN THE RANGE OF 0.010 TO 0.050 INCH, THE WEIGHT OF THE FABRIC BEING LESS THAN 10 OUNCES PER SQUARE YARD, THE BREAKING STRENGTH OF THE FABRIC BEING GREATER THAN 35 POUNDS PER INCH IN BOTH WARP AND FILLING, A SUBSTANTIAL PORTION OF THE YARN CARRYING A THIN COATING OF METAL ON THE SURFACE THEREOF. 